Useful visual outcomes after treatment of Bacillus cereus endophthalmitis

Endophthalmitis Caused by Bacillus cereus: Clinical Characteristics, Outcomes and Antibiotic Susceptibility

Bacillus cereus endophthalmitis is a severe vision-threatening disease. This study aimed to analyze the clinical characteristics, antibiotic susceptibility, and risk factors for poor final visual acuity (VA) and enucleation or evisceration (ENEV) outcomes of B. cereus endophthalmitis patients. We retrospectively reviewed 52 cases (52 eyes) of culture-proven B. cereus endophthalmitis at Zhongshan Ophthalmic Center from January 2013 to December 2023. The mean age of the patients was 38.1 ± 20.1 years, and males composed the majority (90.4%) of the sample size; laborers (32.7%) and farmers (19.2%) were the primary occupations of the patients. All cases were caused by ocular trauma. Forty-one of 51 eyes (80.4%) had a final VA worse than the ability to count fingers (CFs), and 15 of the 52 total eyes (28.8%) underwent ENEV. Binary logistic forward (LR) regression analysis demonstrated that red eye (odds ratio [OR], 13.13; 95% confidence interval [CI], 1.58-108.80; p = 0.017), eye pain (OR, 22.87; 95% CI, 1.00-522.72; p = 0.050), and corneal edema/ulcer (OR, 13.13; 95% CI, 1.58-108.80; p = 0.017) were significant risk factors for poor VA outcomes. Conjunctival sac purulent discharge (OR, 10.08; 95% CI, 2.11-48.12, p = 0.004) and white blood cell (WBC) count (OR, 1.35; 95% CI, 1.06-1.72, p = 0.016) were significant risk factors for ENEV outcomes. B. cereus showed susceptibility rates of 100.0% to vancomycin and ofloxacin; 98.0% to levofloxacin; 93.3% to ciprofloxacin; 87.5% to imipenem; and 78.9% to tobramycin. The susceptibility to azithromycin and clindamycin was 66.7% and 50.0%, respectively. In contrast, B. cereus was resistant to penicillin (susceptibility at 3.8%), cefuroxime (5.6%), and cefoxitin (37.1%).

Recent Updates on Treatment of Ocular Microbial Infections by Stem Cell Therapy: A Review

Ocular microbial infection has emerged as a major public health crisis during the past two decades. A variety of causative agents can cause ocular microbial infections; which are characterized by persistent and destructive inflammation of the ocular tissue; progressive visual disturbance; and may result in loss of visual function in patients if early and effective treatments are not received. The conventional therapeutic approaches to treat vision impairment and blindness resulting from microbial infections involve antimicrobial therapy to eliminate the offending pathogens or in severe cases; by surgical methods and retinal prosthesis replacing of the infected area. In cases where there is concurrent inflammation, once infection is controlled, anti-inflammatory agents are indicated to reduce ocular damage from inflammation which ensues. Despite advances in medical research; progress in the control of ocular microbial infections remains slow. The varying level of ocular tissue recovery in individuals and the incomplete visual functional restoration indicate the chief limitations of current strategies. The development of a more extensive therapy is needed to help in healing to regain vision in patients. Stem cells are multipotent stromal cells that can give rise to a vast variety of cell types following proper differentiation protocol. Stem cell therapy shows promise in reducing inflammation and repairing tissue damage on the eye caused by microbial infections by its ability to modulate immune response and promote tissue regeneration. This article reviews a selected list of common infectious agents affecting the eye; which include fungi; viruses; parasites and bacteria with the aim of discussing the current antimicrobial treatments and the associated therapeutic challenges. We also provide recent updates of the advances in stem cells studies on sepsis therapy as a suggestion of optimum treatment regime for ocular microbial infections.

CLINICAL PRESENTATION, MICROBIOLOGIC PROFILE AND FACTORS PREDICTING OUTCOMES IN BACILLUS ENDOPHTHALMITIS

PURPOSE

To describe the clinical presentation, microbiologic profile, and factors predicting outcomes in Bacillus endophthalmitis.

METHODS

Retrospective interventional case series. Eighty-six patients with culture-proven Bacillus endophthalmitis, from January 2001 to December 2015, underwent vitrectomy/vitreous biopsy and intravitreal antibiotic with or without steroid as appropriate. The undiluted vitreous biopsy was subjected to microbiologic evaluation. The duration of symptoms, presenting visual acuity, organisms isolated, influence of intravitreal dexamethasone with intravitreal antibiotics, and type of initial intervention were examined for any clinical and statistical correlation in terms of odds ratio with the final visual outcome.

RESULTS

Trauma was the commonest etiology (n = 75; 87.2%). Mixed infection with other bacteria was seen in 11 patients. All Bacillus species were sensitive to gentamicin followed by ciprofloxacin (n = 85; 98.83%) and vancomycin (n = 81; 94.18%). Odds in favor of a favorable visual outcome were seen with clinical treatment within 48 hours of the symptoms (OR 25.47, 95% CI 2.45-254.16, P = 0.006), better presenting vision (OR 31.21, 95% CI 2.96-323.64, P = 0.004), and absence of polymicrobial infection (OR 18.03, 95% CI 0.9-344.4, P = 0.05). Only 20% of all treated patients regained ambulatory vision, and one fifth of all of them developed phthisis.

CONCLUSION

Patients diagnosed with Bacillus endophthalmitis merit aggressive vitreous intervention guided by the culture-sensitivity report. Despite early and appropriate treat ment, the outcomes are generally poor.

A multicentre prospective study of post-traumatic endophthalmitis

PURPOSE

Study the clinical and microbiological characteristics and the prognostic factors of post-traumatic endophthalmitis.

METHODS

Seventeen eyes were included between 2004 and 2010, with clinical and microbiological data collected prospectively. Conventional cultures and panbacterial PCR were performed on aqueous and vitreous samples.

RESULTS

Clinical signs of endophthalmitis were observed soon after trauma (1.5 ± 2.5 days). Laceration with an intraocular foreign body (IOFB) was noted in 53% of the patients. At admission, all patients had aqueous humour (71%) and/or vitreous (53%) samples. Fifteen patients (88%) underwent a pars plana vitrectomy. Bacteria were identified in 77% of the cases: Staphylococcus epidermidis (n = 5), Streptococcus (n = 4), Bacillus (n = 2), Pseudomonas stuzeri (n = 1), and Streptococcus salivarius and Gemella haemolysans (multibacterial infection, n = 1). Progression toward phthisis was observed in 35% of the cases; 41% of the patients recuperated visual acuity (VA) ≥20/40. A good final visual prognosis (≥20/40) was significantly associated with initial VA better than light perception (0% versus 70%, p = 0.01) and absence of pupillary fibrin membrane (80% versus 20%, p = 0.05). There was no correlation between visual prognosis and age, the type of laceration (corneal or scleral) or presence of an IOFB. We found a statistical trend toward an association between bacterial virulence and poor final VA.

CONCLUSION

This series showed that better final VA outcomes were associated with initial VA better than light perception, S. epidermidis or culture-negative cases and absence of retinal detachment during the clinical course.

Bacillus cereus, a volatile human pathogen

Bacillus cereus is a Gram-positive aerobic or facultatively anaerobic, motile, spore-forming, rod-shaped bacterium that is widely distributed environmentally. While B. cereus is associated mainly with food poisoning, it is being increasingly reported to be a cause of serious and potentially fatal non-gastrointestinal-tract infections. The pathogenicity of B. cereus, whether intestinal or nonintestinal, is intimately associated with the production of tissue-destructive exoenzymes. Among these secreted toxins are four hemolysins, three distinct phospholipases, an emesis-inducing toxin, and proteases. The major hurdle in evaluating B. cereus when isolated from a clinical specimen is overcoming its stigma as an insignificant contaminant. Outside its notoriety in association with food poisoning and severe eye infections, this bacterium has been incriminated in a multitude of other clinical conditions such as anthrax-like progressive pneumonia, fulminant sepsis, and devastating central nervous system infections, particularly in immunosuppressed individuals, intravenous drug abusers, and neonates. Its role in nosocomial acquired bacteremia and wound infections in postsurgical patients has also been well defined, especially when intravascular devices such as catheters are inserted. Primary cutaneous infections mimicking clostridial gas gangrene induced subsequent to trauma have also been well documented. B. cereus produces a potent beta-lactamase conferring marked resistance to beta-lactam antibiotics. Antimicrobials noted to be effective in the empirical management of a B. cereus infection while awaiting antimicrobial susceptibility results for the isolate include ciprofloxacin and vancomycin.

Endophthalmitis: a review of current evaluation and management

PURPOSE

To review the current state of evaluation and management of various forms of endophthalmitis.

METHODS

A review of the literature is included, encompassing endophthalmitis occurring after ocular surgeries, intravitreal injection, trauma, and systemic infection. Based on this review, current principles and techniques for evaluating and treating these forms of endophthalmitis are discussed.

RESULTS

Postoperative endophthalmitis after cataract surgery is the most common presentation. Conclusions from the Endophthalmitis Vitrectomy Study (EVS) remain a foundation for management of postcataract surgery endophthalmitis, notably prompt intravitreal antibiotic administration after vitreous sampling, with consideration for pars plana vitrectomy in severe cases. The potential impact of advances since the EVS, such as oral fourth generation fluoroquinolones and new vitrectomy techniques, are also discussed. The management of postcataract endophthalmitis is compared and contrasted to endophthalmitis occurring after other ocular surgeries, intravitreal injection, trauma, and systemic infection. Although some principles remain common, treatment rationales differ with other forms of endophthalmitis based on differing clinical circumstances, such as the virulence of organisms that are frequently encountered.

CONCLUSIONS

Endophthalmitis is a serious, potentially vision threatening condition which can present in various settings. Prompt recognition and treatment are key in maximizing outcomes.

Effects of intravitreal moxifloxacin and dexamethasone in experimental Staphylococcus aureus endophthalmitis

PURPOSE

To evaluate the effects of intravitreal moxifloxacin and moxifloxacin and dexamethasone combination in an experimental rabbit model of Staphylococcus aureus endophthalmitis.

METHODS

The right eyes of 24 rabbits weighing 2 to 3 kg were used. Ten thousand colony-forming units (CFU) of S. aureus in 0.1 ml saline solution were inoculated into the vitreous cavity. The eyes were randomly assigned to one of the four groups equally. Twenty-four hours after the inoculation of S. aureus, group 1 received 50 microg moxifloxacin, group 2 received 50 microg moxifloxacin plus 400 microg dexamethasone, and group 3 received 1 mg vancomycin intravitreally. No treatment was given to group 4. Clinical examination scores were recorded. Vitreous aspirates were obtained for microbiological analysis just before sacrifice, and the eyes were enucleated for histopathologic examination. Statistical analysis was performed using Kruskal-Wallis and Mann-Whitney U tests.

RESULTS

In all treatment groups, mean number of CFU and histopathologic score were significantly lower compared with control group (p<0.05), and the difference between treatment groups was not statistically significant (p>0.05). The clinical score was not significantly different between groups (p>0.05).

CONCLUSIONS

Intravitreal injection of 50 microg moxifloxacin was effective in the treatment of S. aureus endophthalmitis. Bacteriological, histopathologic, and clinical outcomes after treatment using moxifloxacin, moxifloxacin and dexamethasone combination, and vancomycin were comparable. Intravitreal moxifloxacin may be an option in the treatment of S. aureus endophthalmitis.

Treatment of Staphylococcus epidermidis endophthalmitis with intravitreal moxifloxacin in a rabbit model

Staphylococcus epidermidis is one of the most common causes of postoperative infectious endophthalmitis, which is a serious complication of ocular surgery and penetrating trauma. Moxifloxacin is a newly developed fluoroquinolone with a potent antimicrobial activity. Corticosteroids are used in endophthalmitis to suppress devastating intraocular inflammatory response. This study was designed to assess the efficacy of intravitreal moxifloxacin alone and in combination with intravitreal dexamethasone. To the best of our knowledge, there is no published report demonstrating the effect of intravitreal moxifloxacin on bacterial endophthalmitis. One eye of each rabbit (n=24) was infected by inoculation of 10(5) colony-forming units (CFU) of S. epidermidis into the vitreus cavity. Rabbits received intravitreal injection of moxifloxacin (50 microg) or a combination of moxifloxacin (50 microg) and dexamethasone (400 microg). No treatment was given to control group. Clinical and histopathological examination scores and microbiological analysis of vitreus aspirates were compared. In the treatment groups, the clinical and histopathological scores and mean CFU were significantly lower than those in the control group (p <0.05) but showed no significant difference between the treatment groups. These results suggest that intravitreal injection of moxifloxacin is effective against S. epidermidis in this experimental rabbit model. Moxifloxacin may be a promising agent in the treatment of bacterial endophthalmitis.

Open globe injuries with positive intraocular cultures: factors influencing final visual acuity outcomes

PURPOSE

To investigate the clinical features influencing final visual acuity outcomes of eyes with positive intraocular cultures after open globe injuries.

DESIGN

Retrospective, consecutive, interventional case series.

PARTICIPANTS

Thirty-seven patients.

METHODS

The medical records were reviewed of all patients with positive intraocular cultures after open globe injuries treated at Bascom Palmer Eye Institute between January 1, 1995, and December 31, 2001.

MAIN OUTCOME MEASURES

Final visual acuity. Clinical features investigated included the following: (1). presence or absence of clinical endophthalmitis; (2). virulence of the cultured organism (coagulase-negative Staphylococci, Corynebacterium, and Propionibacterium acnes were classified as nonvirulent organisms, whereas all other organisms were classified as virulent organisms); (3). presence of intraocular foreign body (IOFB); (4). presence of retinal detachment; (5). interval between ocular injury and surgical repair; (6). severity of vision loss at presentation; (7). zone of injury; (8). wound length; and (9). presence of vitreous hemorrhage.

RESULTS

The study included 37 eyes of 37 patients with a mean age of 30 years (range, 18 months-85 years) and a median follow-up of 13 months (range, 1-71 months). Study eyes were stratified into two groups: group 1 eyes (n = 16) were those in which clinical endophthalmitis did not develop, whereas group 2 eyes (n = 21) were those in which clinically diagnosed endophthalmitis developed at some point during their clinical course. Presenting visual acuity was similar in the two groups (mean logarithm of the minimum angle of resolution [logMAR] acuity, 1.91 and 2.22 [Snellen equivalents, 2/162 and 2/331] respectively; P = 0.33). Final acuities in the two groups were different, but not to a statistically significant level (mean logMAR acuity, 1.14 and 2.05 [Snellen equivalents, 20/276 and 2/224], respectively; P = 0.069). In group 1, final visual acuity ranged from 20/20 to no light perception (median acuity, 20/186); 12 eyes (75.0%) achieved a final visual acuity of 20/400 or better. In group 2, final visual acuity ranged from 20/25 to no light perception (median acuity, 7/200); of 20 eyes with known final visual acuity, 10 (50.0%) retained 20/400 or better vision. In group 1, three eyes (19%) eyes had virulent organisms, and 13 eyes (81%) had nonvirulent organisms. In group 2, 12 eyes (57%) had virulent organisms, and nine eyes (43%) had nonvirulent organisms. A final acuity of 20/60 or better was achieved in 14 eyes (41%), and a final acuity of 20/400 or better was achieved in 22 eyes (59%). Better presenting visual acuity (P = 0.038), culture of a nonvirulent organism (P = 0.011), lack of a retinal detachment (P = 0.002), absence of clinical endophthalmitis (P = 0.069), and shorter wound length (P = 0.024) were associated with better visual acuity outcome. In four of six eyes (67%) with both an IOFB and clinical endophthalmitis (group 2), the final visual acuity was no light perception (IOFB was not itself significantly associated with final visual acuity; P = 0.11).

CONCLUSIONS

Among eyes with positive intraocular cultures after open globe injury, the visual prognosis is guarded. Clinical features associated with better visual acuity outcomes include better presenting visual acuity, culture of a nonvirulent organism, lack of a retinal detachment, absence of clinical endophthalmitis, and shorter wound length.

Infective endophthalmitis caused by Bacillus cereus after cataract extraction surgery

We describe a 72-year-old Chinese man who developed fulminant Bacillus cereus endophthalmitis 36 h after an uneventful surgery for cataract extraction. Clinical progression of disease was extremely rapid, in spite of early vitrectomy and intravitreal injection of antibiotics. Results of Gram staining showed gram-positive bacilli, and the culture was positive for B. cereus. Endophthalmitis is rare after cataract surgery (cumulative probability within 1 year, approximately 0.08%), and cases caused by B. cereus are even less common. The prognosis and plan of treatment are discussed.

Antibiotic therapy in post-operative endophthalmitis

Endophthalmitis following routine cataract surgery is a rare but potentially devastating complication resulting in severe vision loss. Various prophylaxis treatments have been tried. However, none have been demonstrated to completely eliminate the risk. The Endophthalmitis Vitrectomy Study (EVS) helped establish clinical guidelines in the treatment of post-operative endophthalmitis in a prospective, randomized, multicenter trial. The strength and limitation of the study will be discussed as well as the current knowledge of the pharmacokinetics of intravitreous injection of antibiotics. Additionally, the common pathologic organisms, the use of antibiotic therapy, steroids, and vitrectomy will be discussed.

Endophthalmitis after deadly-weapon-related open-globe injuries: risk factors, value of prophylactic antibiotics, and visual outcomes

PURPOSE

To identify clinical and microbiologic factors influencing the prevalence and visual outcomes in endophthalmitis after deadly-weapon-related open-globe injuries.

METHODS

In a retrospective study of 228 eyes of 212 patients with deadly-weapon-related open-globe injuries, clinical and microbiologic factors influencing the prevalence and visual outcome in endophthalmitis were analyzed in detail.

RESULTS

Twenty-nine eyes enucleated for irreparable damages at presentation were excluded. Nineteen eyes (18 patients) of 199 (186 patients) were associated with culture-proven endophthalmitis. Presence of grade 4 injury, a variable of Ocular Trauma Classification System, and lens disruption at presentation were the significant risk factors for development of endophthalmitis (P =.001; odds ratio = 15.9 [2.0 to 122.1]), and ([P <.001; odds ratio = 17.7 [2.3 to 136.3]), respectively. Favorable outcome (visual acuity of 5/200 or better) was achieved in only four eyes (21%). Five eyes (26.3%) were phthisical, and five eyes (26.3%) were enucleated or eviscerated. All eyes were under the coverage of prophylactic intravenous antibiotics when culture positivity was obtained. Except two eyes with Acinetobactersp., all were infected by gram-positive micro-organisms (89.5%), the most common of which (42%) was Staphylococcus epidermidis. None of the clinical characteristics and treatment modalities affected final visual outcome. Favorable outcome was associated with infection by the less virulent micro-organism S. epidermidis (P =.018; odds ratio = 0.50 [0.25 to 1.00]).

CONCLUSIONS

Endophthalmitis after deadly-weapon-related open-globe injuries has a dismal visual prognosis. Severity of injury and lens disruption are significant risk factors for development of endophthalmitis. Infection with a less virulent microbe is the only factor associated with favorable outcome.

Bacterial endophthalmitis: epidemiology, therapeutics, and bacterium-host interactions

Endophthalmitis is a severe inflammation of the interior of the eye caused by the introduction of contaminating microorganisms following trauma, surgery, or hematogenous spread from a distant infection site. Despite appropriate therapeutic intervention, bacterial endophthalmitis frequently results in visual loss, if not loss of the eye itself. Although the pathogenicity of bacterial endophthalmitis has historically been linked with toxin production during infection, a paucity of information exists as to the exact mechanisms of retinal toxicity and the triggers for induction of the intraocular immune response. Recently, research has begun to examine the bacterial and host molecular and cellular events that contribute to ocular damage during endophthalmitis. This review focuses on the causative agents and therapeutic challenges of bacterial endophthalmitis and provides current data from the analysis of the role of bacterial virulence factors and host inflammatory interactions in the pathogenesis of eye infections. Based on these and related studies, a hypothetical model for the molecular pathogenesis of bacterial endophthalmitis is proposed. Identifying and understanding the basic mechanisms of these bacterium-host interactions will provide the foundation for which novel, information-based therapeutic agents are developed in order to prevent vision loss during endophthalmitis.

Clinical profile and outcome in Bacillus endophthalmitis

OBJECTIVE

To study the clinical presentation, microscopic and organismal culture correlation of vitreous, and species-specific outcome in Bacillus endophthalmitis

DESIGN

Retrospective noncomparative case series.

INTERVENTION

Thirty-one culture proven Bacillus endophthalmitis patients between January 1991 and February 1998 underwent vitrectomy and intravitreal antibiotic injection. Lensectomy was combined when considered essential, and on a few occasions intravitreal dexamethasone was added. The patients also received topical and systemic antibiotics. The undiluted vitreous biopsy was the source for microbiologic evaluation (microscopy and culture sensitivity).

MAIN OUTCOME MEASURES

The duration of symptoms, the presenting visual acuity, and influence of intravitreal dexamethasone with intravitreal antibiotics were examined for any statistical correlation with the final visual acuity.

RESULTS

Trauma was the major cause of infection. Vitreous biopsy microscopy demonstrated gram-positive bacillus in 28 of 31 cases, and polymicrobial infection was seen in 12 instances. All Bacillus species were sensitive to gentamicin, followed by vancomycin and ciprofloxacin. Clinical treatment within 7 days of symptoms, use of intravitreal vancomycin, and absence of polymicrobial infection were associated with better visual outcome.

CONCLUSIONS

With appropriate treatment that essentially consists of vitrectomy and intravitreal antibiotics, patients with Bacillus endophthalmitis are likely to benefit in many instances. Gram-positive bacilli detected on vitreous microscopy should be empirically treated as Bacillus species unless otherwise proved.

Vancomycin levels in human aqueous humour after intravenous and subconjunctival administration

The purpose of the present study was to evaluate the level of vancomycin in human aqueous humour after intravenous (i.v.) and subconjunctival administration. One hundred patients scheduled to undergo cataract extraction participated in the study. Fifty-three of them received 20 mg vancomycin subconjunctivally and 47 received two doses of vancomycin i.v. (1 g b.i.d.). Specimens of aqueous humour from the first group were collected 1, 2, 2.5, 3, 3.5, 5, 6, 7, and 8 h after the subconjunctival injection. In the second group, specimens of blood and aqueous humour were collected 1, 2, 4, 6, 8, 10, and 12 h after the end of infusion of the second dose of the antibiotic. The levels of vancomycin were determined by fluorescent polarization immunoassay. In the first group peak levels of 24.82+/-3.55 microg/ml were achieved in aqueous humour at 5 h, whereas in the second group peak levels of 1.42+/-0.47 microg/ml were detected at 6 h. The latter levels, although higher than the MICs of most of the Gram-positive pathogens causing eye infections, are inadequate for the treatment of infections in vivo. These results support the need for subconjunctival instead of i.v. administration of vancomycin in order to achieve therapeutic levels of the drug in human aqueous humour or for prophylactic use whenever indicated.

Endophthalmitis

Endophthalmitis is an inflammatory reaction of intraocular fluids or tissues. Infectious endophthalmitis is one of the most serious complications of ophthalmic surgery. Occasionally, infectious endophthalmitis is the presenting feature of an underlying systemic infection. Successful management of infectious endophthalmitis depends on timely diagnosis and institution of appropriate therapy. Recognition of the different clinical settings in which endophthalmitis occurs and awareness of the highly variable presentation it may have facilitate timely diagnosis. Biopsy of intraocular fluid/tissue is the only method that permits reliable diagnosis and treatment. The different presenting clinical settings, a rational approach to diagnosis (i.e., when, what, and how to biopsy), and the treatment of infectious endophthalmitis are reviewed.

Purification and partial characterization of a neutral protease from a virulent strain of Bacillus cereus

The factors involved in the pathogenesis of Bacillus cereus (B. cereus) in non-gastrointestinal diseases are poorly investigated. Some researchers suggest that B. cereus proteases may be involved in these illnesses. The aim of this work was to purify and characterize a protease isolated from a virulent strain of B. cereus to explain its assumptive damaging effect. The enzyme was purified in a four-step procedure involving ammonium sulfate fractionation, acetone precipitation, Bio-Gel filtration and column chromatography on DEAE-cellulose (DE-52 cellulose). The enzyme appeared homogenous using disc electrophoresis. The specific activity of the protease was 72 U/mg of protein. The enzyme was shown to have a relative molecular mass of 29 kDa. The protease was most active at pH 7.0 and 40 degrees C with haemoglobin as the substrate. The enzyme was made completely inactive by ethylenediaminetetraacetic acid (EDTA), beta-mercaptoethanol, dithiothreitol (DTT) and benzamidine (at a concentration of 1 mM) and by diisopropylfluorophosphate (DIPF), L-cysteine, L-histidine, 1,10-phenanthroline (at a concentration of 10 mM). Divalent cations, especially Ca2+ increased enzyme activity. The enzyme hydrolysed haemoglobin, albumin and casein as the substrates. With haemoglobin and albumin as the substrates Michaelis-Menten kinetics was observed. The obtained Km values were 86 +/- 40 microM (SD, n = 3) and 340 +/- 100 microM (SD, n = 3) for haemoglobin and albumin, respectively. The corresponding Vmax values were 1.26 +/- 0.1 (SD, n = 3) and 0.38 +/- 0.07 (SD, n = 3) mumol of tyrosine liberated per min, per ml, and per mg, while those for casein were not determined. It is concluded that this enzyme is a metal-chelator-sensitive, neutral protease damaging haemoglobin and albumin.